Narrated Khãlid bin Aslam:
Wewent out with 'Abdullãh bin 'Umar and hesaid, "This (Verse) was revealed before theprescription of Zakat, and when Zakãt wasprescribed, Allah made it a means ofpurifying one's wealth." (DE)
USC-MSA web (English) reference: Vol. 1, Book 60, Hadith 183 (DE)
Arabic reference (DE): Book 65, Hadith 4661 (DE)